title: Scope and mechanism of carbohydrase action. Stereocomplementary hydrolytic and glucosyl-transferring actions of glucoamylase and glucodextranase with alpha- and beta-D-glucosyl fluoride.
abstract: Rhizopus niveus glucoamylase and Arthrobacter globiformis glucodextranase, which catalyze the hydrolysis of starch and dextrans, respectively, to form D-glucose of inverted (beta) configuration, were found to convert both alpha- and beta-D-glucosyl fluoride to beta-D-glucose and hydrogen fluoride. Each enzyme directly hydrolyzes alpha-D-glucosyl fluoride but utilizes th beta-anomer in reactions that require 2 molecules of substrate and yield glucosyl transfer products which are then rapidly hydrolyzed to form beta-D-glucose. Various D-glucopyranosyl compounds serve as acceptors for such reactions. Mixtures of beta-D-glucosyl fluoride and methyl-alpha-D-glucopyranoside[14C], incubated with either enzyme, yielded both methyl-alpha-D-glucopyranosyl-(1 leads to 4)-alpha-D-[14C]glucopyranoside and methyl-alpha-D-glucopyranosyl-(1 leads to 6)-alpha-D-[14C]glucopyranoside. Glucoamylase produced more of the alpha-maltoside; glucodextranase produced more of the alpha-isomaltoside. Thus, both "exo-alpha-glucan hydrolases" emerge as glucosylases that catalyze stereospecifically complementary hydrolytic and transglucosylative reactions with glucosyl donors of opposite configuration. These reactions not only provide a new view of the catalytic capabilities of these supposedly strict hydrolases; they also furnish a basis for defining a detailed mechanism for catalysis. Present results, together with those of several recent studies from this laboratory (especially similar findings obtained with beta-amylase acting on alpha- and beta-maltosyl fluoride (Hehre, E. J., Brewer, C. F., and Genghof, D. S. (1979) J. Biol. Chem. 254, 5942-5950), provide strong new evidence for the functional flexibility of the catalytic groups of carbohydrases.
mesh_terms: D001173:Arthrobacter / Q000201:enzymology*; D005087:Glucan 1,4-alpha-Glucosidase / Q000378:metabolism*; D005936:Glucans / Q000378:metabolism; D005947:Glucose / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D005959:Glucosidases / Q000378:metabolism*; D006027:Glycosides / Q000378:metabolism; D006858:Hydrofluoric Acid; D007700:Kinetics; D008757:Methylglucosides / Q000378:metabolism / Q000494:pharmacology; D012233:Rhizopus / Q000201:enzymology*; D013237:Stereoisomerism
chemical_list: D005936:Glucans; D006027:Glycosides; D008757:Methylglucosides; C030364:glucosyl fluoride; D005959:Glucosidases; D005087:Glucan 1,4-alpha-Glucosidase; C023149:exo-1,6-alpha-glucosidase; D005947:Glucose; D006858:Hydrofluoric Acid